The present disclosure relates to circuitry for supplying power to gas discharge lamps such as fluorescent lamps which generally require the generation of a relatively high voltage AC current for effecting operation of the lamp. Typically, the power circuitry for the gas discharge lamp includes a way of stepping up the power line or input voltage to the required level for effecting discharge of the lamp and the circuitry often includes a transformer and a ballast or driver circuit with a pulse generator or igniter “ON” circuit which usually includes a transformer. The circuitry required to effect operation of gas discharge lamps is thus somewhat complex and relatively costly and further provides only a single power level of operation for the lamp, generally at its rated current capacity. In order to improve the usage of gas discharge lamps and further reduce the power required for their operation, it has been desired to provide a low cost, simple and effective way of operating a gas discharge lamp at less than full current capacity where reduced illumination is needed during certain periods of operation to reduce the power consumption during such periods.
Referring to FIG. 7, a prior art circuit arrangement for powering gas discharge lamps such as fluorescent lamps is shown schematically in which a relatively low voltage direct current power supply is applied to the parallel coupled inductors L1, L2 which are connected to switching transistors Q1 and Q2. The base drive signals of Q1 and Q2 are typically generated from the primary windings of a transformer T1 and in conjunction with the diodes D1, D2 form a half bridge circuit. The alternative switching of Q1 and Q2 provides an AC current on the primary of T1 and generates a constant stepped up voltage on the secondary of T1, the frequency of which is determined by the resonant frequency of the circuit based upon L1, L2, C3, C4, output capacitor and the inductance of the transformer T1.
The circuitry of FIG. 7 is typically employed for what is commonly referred to as an instant-start ballast for a fluorescent lamp. The aforesaid ballast circuitry of the prior art for gas discharge lamps has thus provided a dedicated level of power input to the lamp through a given power line condition; whereas, it has been desired to provide a simple, low-cost way of enabling users of such gas discharge lamps to reduce the power input thereto and yet provide adequate power to effect illumination of the lamp albeit at a lower level.